This application claims the priority of German Application No. 101 40 299.6-52, filed Aug. 16, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for monitoring plasma or flame-spray processes.
A method for contemporaneous (on-line) measurement of powder spray particles in a plasma beam is known from European Patent EP 0 542 542 B1. The luminous radiation emitted by the plasma beam is focused on the end of a fiber optical waveguide. At the other end of the fiber optical waveguide, the luminous radiation is divided into two light beams, each of which is fed into a photo detector, by means of a dichroic lens. In the photo detectors, the intensity distribution over time is determined for each light beam. A filter installed ahead of the photo detectors provides that suitable wavelength ranges can be filtered out of the luminous radiation and their intensity progression over time determined.
European Patent EP 0 542 542 B1 also describes the option of using a waveguide bundle and of feeding the received radiation to a CCD camera.
Another method for determining the intensity distribution over time of luminous radiation emitted by plasma is known from U.S. Pat. No. 5,986,277.
The disadvantage of these known methods is that it is only possible to determine the intensity distribution of the luminous radiation of the plasma. In addition, only the velocity and temperature of the particles can be determined with the known methods. Consequently, the known methods allow for only limited monitoring and diagnosis of the contemporaneous plasma condition. It is not possible to monitor the other process parameters relevant to the spraying process. In addition to those described above (velocity and temperature of the particles), the process parameters that define the plasma condition include plasma composition, composition of the spraying materials, and the flow of the melt and other materials.
The object of the invention is to provide a method which makes it possible to determine other parameters contemporaneously, in addition to the velocity and temperature of the particles.
According to the invention, the luminous radiation is reproduced on one end of the optical fibers arranged in a one-dimensional or two-dimensional array. In addition, also according to the invention, spectral analysis of the luminous radiation transmitted in the optical fiber is accomplished with a spectrometer arranged at the other end of the optical fiber. The spectrums are analyzed in a processor, such as a data processing system, to determine the process parameters of the spraying process. The analysis of the spectrums is accomplished with a method known to a person skilled in the art.
In contrast to the prior art, the progression of an entire spectrum over time can be determined for any optical fiber with the method of the invention. A spectral resolution of individual image points (formed by the individual optical fibers) along the plasma beam can be achieved with the spectrometer. Because of its small size, a spectrometer positioned on a plug-in card for a data processing system (PC) can advantageously be used as the spectrometer.
It is also possible to identify power spray materials as well as gas and liquid precursors, as well as to determine their progression over time, based on characteristic spectral lines in the measured spectrums. The corresponding spectral lines can be independently determined for each optical fiber. Consequently, it is especially possible to examine the plasma beam over space and time with respect to its contemporaneous process condition by means of the process of the invention.
Another advantage of the present invention is the ability to simultaneously determine the velocities of several different particles contained in the plasma beam. Several different gas and material flows in the plasma beam can also be determined simultaneously. This is especially advantageous when not only a powder material, but also, for example, a powder mixture is used as the spraying material.
The method of the invention can also be used to determine the stability of the plasma beam, which exerts a decisive influence on the quality of the spraying process.
In an advantageous embodiment of the invention, it is possible to sequentially feed the luminous radiation of the individual optical fibers in the array of the invention to a single spectrometer. This array can, in particular, be a linear array or a square or rectangular array, such as one with a 4xc3x974 or 5xc3x975 matrix.
In this process, each optical fiber in the array is sequentially scanned, so that the luminous radiation is sequentially fed into the spectrometer. The advantage of this process lies in substantial space and cost savings with respect to the components required for the process. Switching the individual optical fibers to the spectrometer can be accomplished without significant loss of time by means of switches known to the person skilled in the art.
Thus, comprehensive monitoring and on-line diagnosis of a thermal spraying process is possible with the method of the invention.
In another advantageous embodiment of the invention, it is possible to regulate the process parameters of the spraying process by means of the process condition determined on the basis of the spectrums. In doing so, it is, for example, possible to regulate the gas and material flows of the plasma beam and of the spraying material fed into the plasma.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.